ON THE PREPARATION OF SODA AND CHLORINE. 43 



colored green, by dissolved sulphuret of iron, and an insoluble 

 residue, of finely divided sulpburet of iron. Tbis alkaline solution 

 wben exposed to tbe influence of carbonic acid and oxygen, be- 

 comes decolorised, and yields on evaporation carbonate of soda. 

 This method of producing soda was proposed as early as the year 

 1778, by Maleherbe, a Benedictine monk, who however used me- 

 tallic iron instead of the peroxide ; and is the same in principle 

 as that patented in Great Britain, by Blythe and Kopp, in 1856. 

 These patentees prevented the partial solution of the sulphuret 

 of iron by the alkaline liquid, by exposing the melted material to 

 the action of carbonic acid and atmospheric air previous to treat- 

 ing it with water. I have however found that in the simple evap- 

 oration of the solution tbe decolorisation is effected by a separ- 

 ation of the dissolved sulphuret. In carrying out the method on 

 the large scale, the action of the readily fused alkaline mass on the 

 usual furnace materials is found to be very severe. In the course 

 of my experience in refining impure arseniurets of nickel and co- 

 balt, on the large scale, by fusing these with sulphate of soda and 

 charcoal, I ascertained that a furnace bottom consisting principally 

 of ground quicklime, resists the action of the alkaline sulphurets, 

 and I found on smelting the mixture of sulphate of soda, coal and 

 iron oxide above mentioned, in contact with a hearth of the same 

 material, that the latter was not acted on, and thus succeeded in 

 removing one of the greatest practical difficulties which beset 

 this new method of manufacturing soda. 



The residual sulphuret of iron from the soda process, was ac- 

 cording to Blythe and Kopp's patent, utilised by calcining it, and 

 conducting the sulphurous acid thus produced into the leaden 

 chamber, for conversion into sulphuric acid, in the usual manner. 

 This moist sulphuret of iron, however, on being exposed to air 

 and moisture, passes through various intermediate stages of oxi- 

 dation, and finally becomes very rich in sulphate of iron. As 

 this salt finds a ready and suitable application in the new method 

 of producing chlorine, it seemed to me the preferable mode of re- 

 covering the sulphur, to remove the sulphate of iron from the 

 oxidized mass by lixiviation, and to evaporate the solution obtained 

 to crystallization. 



Having thus stated the manner in which this new method of 

 making chlorine and carbonate of soda suggested itself to me, 

 I may be permitted to state, more concisely my manner of put- 

 ting the method into practice, which is as follows : — 828 parts 



